Currently, the majority of the nursery grown landscape plants, such as trees and shrubs, are initially grown in conventional smooth-wall, non-porous containers made of plastic, steel or other materials. The smooth-wall containers, however, tend to deflect root growth, causing it to then follow along the interior surface of the container, or deflect the root around the sidewall creating a root defect. This often results in root circling and a stem girdling root system. Such containers cause the primary roots to revolve around the container, which can cause significant stability problems when the tree matures. Such poor root development and anchorage problems are especially detrimental to trees of the larger variety.
Generally, the roots of a plant grow and extend in a radial fashion from the main stem or trunk. Thus, a root will extend in a naturally promoted direction (i.e., outwardly and downwardly) until it contacts something that it cannot move or penetrate. At that point, the root is deflected in a new direction and extends until it encounters something else that would change its direction of growth or travel. Many seedling woody perennials, in particular, will first develop a tap root that plunges downward. The tap root on some woody perennials will develop a foot of primary root for every inch of top growth. Once the taproot is cut or pruned, the apical dominance of its root tip is lost and the development of some secondary lateral rooting commences. These secondary roots tend to grow a little more horizontally, although generally downwardly, in direction. When these roots run out of room to grow, they begin to circle around the inside of the container. Hence, unless air root pruning is permitted, a phenomenon in which the growth of a root ceases when the root extends into the vicinity of an aperture that is exposed to the atmosphere, these roots will grow to the bottom of the container where they continue to grow in a circular pattern.
Air pruning, hence, is highly desirable, and naturally occurs when roots are exposed to air in the absence of high humidity. The roots are effectively “burned” off, causing the plant to continually produce new and healthy branching roots. If roots are not exposed to air, they continue to grow around the container in a constricted pattern. The roots may spiral, twist, kink or become stem girdling. When such a plant is later installed into the landscape, it will likely fail to establish a normal root structure, and instead will have reduced uptake of water and nutrients. Eventually abnormal growth should be obvious and could cause the plant to fail. Damaged root systems also cause leaves to turn yellow or brown, shrivel or drop. Healthy, highly branched root structures allow a plant to more efficiently uptake water and nutrients while increasing growth and overall plant health. A strong, fibrous radially extending root system will make a plant better able to establish itself when installed in a planting project.
Many plant containers have been developed that attempt to encourage side root growth, via air root pruning, and reduce circling of the roots. For instance, many cylindrical plant containers exist that incorporate small size side apertures in an attempt to inhibit such concentrated spiral and circular root growth. In all these designs, however, the side apertures are relatively small, and are not sufficiently abundant. This is due to the fact that too large and too many apertures will not retain the soil properly, allows the water to pass through the sides too quickly, not allowing the soil to absorb moisture, and accelerates evaporation. Although the mere presence of a side aperture or apertures do function to encourage side root growth, air-pruning of the roots, and initially reduce the incidence of spiraled or circled roots, eventually the small sidewall apertures become filled with roots or the secondary roots the encounter sidewall and deflect, causing spiraling and circling to ensue. The large amounts of obstructive material greatly increase the opportunity for the development of circling and stem girdling roots. Once the apertures have become filled with roots, the opportunity for air pruning is diminished and root circling begins. Typical of such designs are disclosed in U.S. Pat. Nos. 4,442,628; 4,497,132; 4,510,712; 4,753,037; 4,939,865; 5,099,607; 5,131,185; 5,241,784; 5,557,886; and 5,937,577.
Accordingly, it is therefore highly desirable to provide a transplantable plant container that encourages regenerative root growth though the container sidewall, even after air pruning has commenced, until the plant is transplanted or planted into the landscape.
It is further desirable to provide an improved plant container for growing transplantable plants, whereby spiral and circular root growth is reduced or substantially prevented, and the development of lateral root tips at the bottom and around the sides of the container is maximized by air root pruning.
It is still further desirable to provide a plant container that is formed to improved plant growth wherein the production of lateral root tips is promoted at all levels in a plant growth medium and the root tips quickly grow in all natural directions radially from the plants main stem, whereby the plant is quickly laterally anchored when transplanted and maximum water and nutrients are absorbed.
Despite the abundance of container designs available that improve the health of a transplantable plant, there remains a need for a container that enhances root development by air pruning of the roots and significantly prevents circling and stems girding roots.